Key ideas in plain English
A preposition links a noun to the rest of the sentence and shows relations like time, place, topic, cause, method, or agent. A collocation is a word pair that native writers prefer, such as on average or in contrast. An agent in the passive voice is the doer of the action. A medium is the channel used, such as on radio or on the internet.

1) Time: at, on, in, by

• at a clock time or a precise point: at 3 pm, at midnight, at the end of 2024.
• on a day or date: on Monday, on 12 May, on the first day.
• in longer periods: in June, in 2020, in the 1990s, in the long term.
• by a deadline meaning “no later than”: by 2025, by the end of the week.

Useful contrasts

• by vs until: complete the action by Friday vs continue the action until Friday.
• on time vs in time: on time means punctual; in time means before a deadline or just early enough.

2) Place and academic settings: at, on, in

• at a point, institution, or event: at the University of Dhaka, at a conference, at home, at school.
• on a surface or platform: on the table, on page 12, on campus, on the internet, on the map.
• in an enclosed space or a defined area: in a laboratory, in Bangladesh, in the introduction, in Figure 2.

Institutional nuance

• at university means you are a student there.
• at the university refers to the physical site.
• in hospital (as a patient) vs at the hospital (the building or workplace).

3) Topic, medium, and content: on vs in

• on for the topic of a paper or talk: a lecture on climate policy; an article on migration.
• in for the container or source text: in the article, in the report, in Table 3, in Figure 1.
• about is broader and less formal than on for academic titles.

4) Passive agent, method, and cause: by vs with vs using

• by + doer in passive: The policy was approved by the committee.
• by for method without a concrete tool: prove it by induction; travel by bus.
• with + instrument or material: The samples were cut with a laser.
• using is a safe alternative to show procedure: measured using a calibrated scale.

5) Data reporting set: at, by, to, from, in

• Level: X stood at 48 percent in 2020.
• Change-difference: X rose by 5 percentage points.
• Change-destination: X rose to 53 percent.
• Baseline: X increased from 30 to 45.
• Domain: growth in rural households; spending on transport.

6) High-value academic collocations

• on average, on the whole, on balance
• in contrast, in summary, in turn, in addition
• at risk, at scale, at least, at most
• by contrast, by definition, by design

Use these as fixed blocks. Do not swap the preposition.

Two worked examples with notes

Example 1 - Methods and data
Weak: The results were calculated with 2023 and increased till 2024.
Strong: The results were calculated using 2023 data and increased from 2023 to 2024, reaching at most 68 percent by December.
Why: using for method, from-to for span, at most for a cap, by for deadline.

Example 2 - Topic vs container
Weak: In climate change, the author focuses in renewable energy.
Strong: In the article, the author focuses on renewable energy.
Why: in + container, on + topic.

Mini case — Farhan from Dhaka

Problem: Farhan mixed on and in for visuals and misused by vs until in deadlines.
Intervention: he built a 20-line card set with pairs: on page vs in the article, in Figure vs on the map, by 2025 vs until 2025. He added a three-item data check after every Task 1 draft: stood at, rose by, rose to.
Result: preposition errors fell from 10 to 3 per 300 words in two weeks, and his Task 1 band improved from 6.0 to 7.0 in mocks.

Measurable drills

• 10-line container-topic drill: Write five sentences with in + source and five with on + topic. Score 10/10 correct.
• Data trio pass: Underline every change verb and label level at, difference by, destination to. Aim for 100 percent mapping.
• Deadline test: Create six sentences showing by vs until. Read aloud and check meaning contrast.
• Collocation sort: Sort 16 items into at/on/in/by groups. Repeat daily in 90 seconds.

Common mistakes

• on 2020 or at 2020 instead of in 2020.
• at the weekend vs on the weekend confusion across dialects; avoid in the weekend.
• on average written as in average.
• by 10 percent when you mean to 10 percent.
• in the table shows… Prefer Table 2 shows… or as shown in Table 2.

Edge cases and safe choices

• At the beginning vs in the beginning: at the beginning of the semester is temporal position; in the beginning means initially in a narrative.
• On campus vs in campus: use on campus.
• On the internet vs in the Internet: standard modern choice is on the internet.
• Street prepositions: in the street focuses on the area; on the street can mean outdoors or homeless depending on context.
• By which vs in which in relative clauses: choose by which for method, in which for place or container.

Tips and tricks

• Build sentence frames you can recycle: X stood at N percent in YEAR; it rose by P points to M.
• Mark topic vs container during reading: write T on margins for topic phrases with on, C for containers with in.
• Learn fixed collocations as chunks; do not translate from your first language.
• When unsure between with and by for tools, choose with for a physical instrument and by for method or transport.

To avoid

• Mixing container and topic: in the topic of… Use on for topics.
• Overusing about in formal titles; prefer on for paper topics.
• Swapping prepositions in fixed phrases: on average, in contrast, at least, by contrast.
• Writing at Monday or on 2020.

Glossary

Preposition – a linking word that shows relations of time, place, method, topic, or agent.
Collocation – a preferred word pairing used by fluent writers.
Agent – the doer in a passive sentence, introduced with by.
Medium – the channel used for communication.
Container phrase – the source or location of content, often with in.
Data trio – the set at level, by difference, to destination.

Next steps
Take your last Task 1 and Task 2 drafts. Run three passes:

1. Time-place check for at-on-in.
2. Data trio pass for at-by-to-from.
3. Topic-container pass for on vs in.
   Record preposition errors per 300 words now and again after one week. Target a 50 percent reduction.
4. Actionable closing — Myth vs fact

• Myth: on and in are interchangeable for visuals.
  Fact: use in Figure/Table but on the map and on page 12.
• Myth: by is just a fancy word for until.
  Fact: by sets a deadline; until marks a continuing action.
• Myth: about is the best academic topic marker.
  Fact: titles and claims prefer on for topics.
• Myth: with always replaces by for tools.
  Fact: choose with for instruments, by for method or agent.
• Myth: native writers vary prepositions for style.
  Fact: set collocations stay fixed. Write on average, in contrast, at least, by design.

CTA: Print the data trio and collocation list. Edit one 200-word paragraph today and fix every at-on-in-by choice using the passes above. Log your error count and aim to halve it within seven days.